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94               , SHOULDER   GIRDLE   OF   CYWQGJWATjyUS            CHAP.
pared to that "of Tfaylacinus or Dissacus" No one can ex-
amine the actual sketches of the skull of that Theriodont
without endorsing that opinion. As a curious detailed point
of likeness to certain Mammalia may be mentioned " a small
descending process of the malar bone, which may be a diminu-
tive representative of the descending element of the malar
seen in JSlotherium-, NototJieriutn, Diprotodon, Macropus, certain
Edentata, such as Glyptodon, Megatherium, Mylodon, JBradypus,
but unparalleled so far as I am aware in fossil reptiles." (Osborn.)
The zoologist cannob help being impressed with the significance
of small details of similarity, which do not seem to be due in any
way to surrounding conditions of life, and thus referable to mere
convergence, like the fish-like form of Whales and Seals.
The rest of the skeleton of the Theriodontia is by no means
so well known as the skull and teeth. But from what is known,
other mammalian characters can be pointed out. Perhaps the
most striking mammalian feature is to be found in the scapula
of Cynognathus. It is in this creature somewhat narrow and
elongated; but it has a well-marked spine, ending in a hooked
acromion. IsTow it is to be noted in support, so far, of the
diphyletic origin of mammals, that in the Monotreme, as in
Whales indeed, the spine forms the anterior border of the scapula,
and is coincident with it, there being thus no prescapula at
all in the Monotreme, and only a trace of it in certain Whales.1
Whether the multituberculate Tritylodon or Diademodon had
a scapula after the Monotreme pattern is not known; but it is
clear that the scapula of the triconoaont C/ynognathus is quite after
the pattern, of the Eutherian scapula. Furthermore, Professor
Seeley is of opinion that the coracoid was relatively small, and
indeed smaller than the same bone in Edentates, and a fortiori
than in Monotremes. Another fact of structure which points
also, possibly, in the direction of a diphyletic origin for the
Mammalia, is the double-headed ribs of Gynognatl^us. As is well
known, the ribs of the Monotremata have only the central head,
the capitTolrim,
As a general mark of affinity with mammals the reduction of
the  intercentra   in   Cynogntxthus may be noted,  and   also   the
existence of a small though perfectly obvious obturator-foramen,
separating the puMs from the ischium.    There are further details
1 It may be necessary to exclude the Whales from the comparison.